"The last person that saw it was my brother. He drove by on 6:30 Sunday evening, and he said he saw it there. But 10 a.m. Monday when we opened, it was missing," Hammer told ABCNews.com.

Hammer is unsure how anyone would be able to remove or steal such a large pumpkin, since it was a feat even getting it to their own farm stand.

"I picked this up from another farmer farther north in Illinois. I actually had two of them. We sold one, and I didn't want to sell the second one because I thought it would be a good attraction for kids to take pictures with. We wanted to keep one mainly as an attraction," Hammer said.

Although the pumpkin wasn't grown on their own farm, the pumpkin being stolen is still a sore subject for the Hammers.

"When we took it off the truck, we had to use the bucket of the tractor to move it. We had to use the tractor to roll it off onto the pallet," Hammer said. "They'd have to have a truck, or an SUV maybe. It'd have to be multiple people to pick it up. One person wouldn't be able to do it. I'm pretty strong myself and I wouldn't be able to pick it up."

The market is located along a river, not set too far back off the road. The Hammers had the pumpkin sitting out front with a display of mums. They weren't worried about tying the pumpkin down at night, because they thought it would be too big of a burden for anyone to steal.

"I figured someone might try to steal one of the smaller ones, but I didn't think anyone would have the guts to steal one that big," Hammer said.

Now, all that's left where the giant pumpkin used to sit are signs asking people to please be on the lookout for it.

"My mom made a couple of signs right where the pumpkin used to sit: 'Someone stole the great pumpkin, if you could please let us know if you've seen it, we'd love to get it back,'" he said.

A pumpkin this size would typically sell for $40 to $50, but money aside, the Hammers are just baffled at how it disappeared.

"It's a 300-pound pumpkin, so it can't exactly hide. No one else around has a pumpkin this size, so it's pretty obvious where they got it from if I find it," Hammer said.

No ransom money is being offered for the over-sized orange hostage, but Hammer said perhaps they would give the pumpkin-nappers a smaller one for its safe return.